Method of heating



Dec. 16, 1930.

F. l. RAYMOND .METHOD OF HEATING Filed July 16, 1928 4 Sheets-Sheet 2 Dec. 16, 1930. Q RAYMOND 7 1,785,426

- METHOD OF HEATING I Filed July 16, 1928 4 Sheets-Sheet 3 "llil'llllllllii" 3 F. '1. RAYMOND Dec. 16, 1 930.

Patented Dec. 16, 1930 FRED I. RAYMOND, RIVER FOREST,

ILLINOIS METHOD OF HEATING Application filed July 16,

This invention'relates to a new and improved method of heating having for its object the maintenance of a more uniform temperature in the space to be heated-and, incidentally, a reduction inthe amount of fuel consumed.

The method is applicable to heating by means of hot water, hot air or steam as heating media, and can be employed either for direct or indirect systems of heating, and,

in the case of steam, either with high pressure, vacuum or vapor systems. In all cases it is applicable to systems using either solid "fuel, such as coal, or fluid fuels such as gas or oil. 1

The method involves the control of the ap- 'plication of heat to the space heated, in accordance with temperature changes in said space and also in accordance with temperature changes in the heating medium; and

yarying the temperatures at which the heatmg mediumaccelerates and retards the fire (which phrase will be used hereinafter, for brevity, in the specification and claims to mean any increase or decrease in the amount of heat generated or applied to the space heated) in accordance with changes in temperature of the outside atmosphere.

The effect of this method of control is to minimize those fluctuations in the temperature of the space heated that are inherent in any system involving retardation and acceleration of the fire by intermittent action. In any such system the response of the fire, in case of the solid fuel fire when the furnace dampers are opened and closed, will not be immediate. Another factor'of lag is the stored heat in. the heating medium where such medium consists of hot water or steam. There is .also a lag in temperature change as between the source of radiation (radiator or of convection currents (hot air register and the place where' the control instrument is located. In accordance with the present method these fluctuations of temperature in the space vheated,both above and below the a desired temperature, if not entirely eliminated, are reduced to a minimum by the maintenance of the heating medium atall in whic time; and for all weather conditions at tem-- 1928. Serial No. 293,293.

peratures very close to those required for keeping. the temperature of the space heated at the desired level. This cold 70 is effectiveliyl done away'with, that is a condition despite the fact that the room thermostat indicates 70 F. the actual tempera? ture of the room, and particularly the part of the room near the windows where it is customary to locate radiators, isbelow 7 0 F.

The correlation of the two control factors that responsive to fluctuations in the room temperature, and that responsive to temperature fluctuations in the medium as modified by outside temperature -may take different forms according to the particular result desired. For example, (1) the fire may be accelerated only when lower critical temperatures are reached both in the space heated and in the heating medium while the fire .is retarded whenever either upper critical temperature is reached. This means that the heating medium will never exceed a certain maximum, regardless of the requirements for heat of the room.

(2) In accordance with another embodiment of the method the fire will be accelerated whenever either the room temperature or the temperature of the heating medium falls below a certain point while the retardation of the fire is dependent upon both room atmosphere and heating medium being at or above determinate upper temperatures. This means that the radiators (assuming a hot water or steam system) will always be maintained at a certain fixed high temperature even though it may be at the expense of overheating the medium.

(3) These two types of control correlation .may also be combined to obtain, to some extent, the advantages of both.

In any case the adjustments may be such as to give what may be termed point con-v trol sofar as concerns the instrument responsive to changes in room temperature.

In the ordinary thermostatically controlled heating system the room thermostat functionsto accelerate and retard the fire at tem peratures which may be, for instance, two degrees'apa'rt. That is, the fire is accelerated when the room temperature falls, say, to 68 the room temperature reaches, say, Fahrenheit. This will necessarily involve an accentuation ofthe lag as between the desired change in room temperature and the change in the setting of thecontrol instrument.

That is, assuming a straight line to represent the temperature of the heating medium required to maintain the room at the desired temperature the actual'temperature curve of the heating medium will oscillate periodically above and below such line. With what has been termed point control involving alternate retardation and-acceleration whenever room temperature varies from a single point one serious cause of lag as between the functioning of the control mechanism and the response thereto of room temperature is eliminated.

The method will be better understood from- .the following description of its application to the different types of heating systems and to different types ofcontrol correlation which are illustrated diagrammatically in the .ac companying drawings in which: Fig. 1 shows the invention as applied to-a hot water system in' which the medium is heated by a solid fuehfirehaving the first mentioned type of control. v

Fig. 2 shows the application of the method to a water heating system but with one of the control elements in a different position.

Fig. 3 shows a system embodying the second mentioned typeof control correlation.

Fig. 4 illustrates a system combining both types of control correlation.

Fig. 5 illustratest'he. application of the method to a vacuum or vapor steam heating system.

Fig. 6 illustrates its system.

Fig. 7 shows the application of the method to an indirect heating system, sd-called, in which air for heating the room is caused to move past a heating device.

Fig. 8 illustrates a. system in which the control is applied to a multiple oil-burning application to a hot air or gas-burning furnace for accelerating or the fire by control of the'bu'rners retarding singly; and I 3 Fig. 9 illustrates an embodiment of the method in which the control is applied to the radiator of a steam. or va or system to va the extent to which the ra 'ator-will be filled withsteam. Other applications of the'meth'od of practice are possible and it is'r'ny purpose to cover by patent all variations on the methodv as illustrated and hereinafter described, and all applications of the same to practice within the scope of the heretoia'ppended claims.

the motoror other equivatlentdavibe' for con-- trolling the fire under the boiler, the drawing.

day operation of the fire.

illustrating the 'usual periodically actuated motor for a solid fuel furnace having cranks struction. This device may have the usual manual or time adjustment for night and is shown in a conventional manner, 17 being the low temperature contact, 18 the high temperature contact and 19 the heat sensitive circuit closing element or movable contact which vibrates between the fixed contacts 17 and 18.

The compound thermostat designated 20 (by which is intended the instrument responing medium modified by outside temperature) is provided with a low'temperature con-- tact 21, a high temperature contact 22 and a -12, 13 connected by chains 14, 15 with the.

The thermostat sive to temperature fluctuations of the heatcircuit closing element 23 which latter is oscillated by means of a spiral tubular element- 24, the. interior of which is connected by tubes 25, 26 with bulbs 27 and 28, the spiral tubular element, tubes and bulbs containing a fluid which expands and contracts appreciably with changes of temperature. The bulb 27 is arranged so as to respond to temperature changes of the heating medium. It is shown as submerged in the water in boiler 10.

V The bulb 28 is arranged so as to respondto fluctuation in the temperature of the outside atmosphere. The bulb 28 however need not be exposed directly to the outside atmosphere so long as it is so plac'ed as to respond to the temperature changes thereof. The bulbs 27 and 28 may be equal in volumetric contents or different in volumetric contents, in anyproportions, dependent upon the extent to a which it is desired to have changes in outdoor temperature modify the control effected by temperature fluctuations of the heating medium..

The wiring system for the apparatus is .a modificatlon of the common'three-wire syswith the water of the heati system at 170 'tem used in temperature control ap aratuses; A specific example of theoperatlon of the. system is as follows: It will be assumed that Fahrenheitthe heat output 0 the system will be somewhat more than is'necessary under 28 as shown are of the same size,

any conditions to keep the house warm with an I outside temperature-of 0 Fahrenheit. The bulbs 27 an although'this in practice will depend upon' the particularheatin'g plant withwhich the control system is associated. The compound thermostat 20- may be calibratedto function at a low temperature of F. and at a; high i temperature of F. With an outside Referrmgfirst'to Fig. 1,. 10' designates the boiler of a hot water heating-system and 11 temperature of zero the temperature I of the water in boiler 10 will therefore haveto reach outside temperature instead of being zero Fahrenheit is Fahrenheit the boiler temperature need rise only to 110 before the fire is retarded. At 10 below zero. the boiler temperature must be 180 in order to actuate the thermostat to retard the fire. Other outside temperatures will modify the operation of the compound thermostat proportionately. In the drawing the parts of control apparatus are shown" in the positions they will occupy when the heating system is first started up. That is,-the temperature in the room 29 in which thermostat 16 is located is at or below the temperature at which the oscillating member 19 of the thermostat 16 contacts with the low temperature contact 17 The water in the boiler is also below 120 .F.. let us say, assuming for the purpose of illustration an outside temperature of 50 F, If the time be early morning the oscillating member of thermostat 16 has been brought against contact 17 by the timing mechanism of the room thermostat. Under these conditions the fire. is drawing. Thermostat 20 will ordinarily be first to operate. As soon as the water in the boiler reaches a temperature of 120 F. the circuit closing member 23 of thermostat 20 will be moved against the high temperature contact 22 closing a circuit through motor 11 over wires 30 and 31; The closing of this circuit actuates motor 11 to retard the fire. If in the meantime the room temperature has reached 72, the temperature at which the oscillating member 19 is brought into contact with the high temperature con tact point 18, the fire will be retarded by the room thermostat '16 .acting independently of the compound thermostat 20, by the closing of a circuit comprising wires 30, 32, 33 and 31. This circuit includes the low temperature contact 21 of thermostat 20 against which, by supposition, the arm 23 of thermostat 20 lies. Ordinarily however thermostat 20 will function several times to retard and accelerate the fire before the temperature of the room 29 will have risen to a point to break the circuit at 1917. The thermostat 20 operates to accelerate the fire when the heating medium cools to 160 F.- by closing at 23-21 a circuitcomprising wire 34, low temperature. contact 17 .of the room thermostat 16, movable contact member 19 of thermostat 16, wire 33, low temperature contact 21 of thermostat 20, movable contact member 23 of thermostat 20 and wire 31..

This fire accelerating circuit includes, it will be seen, the low temperature contacts of both thermostats so that while either thermostat canretardthe fire, depending upon whether the circulating water is first to heatup to its.

maximum critical temperature or the room temperature heats up to its maximum critical temperature, both water and room temperatures must be at or below their minimum critical temperatures .in order that the fire" should be accelerated. Instarting up the system in the morning the water will be heated up to 120 (on the conditions assumed) several times before the room thermostat breaks the on circuit at 19-17. The room thermostat merelv puts a check upon the compound thermostat, reventing such overheating as might occur liecause of the fact that the compound thermostat is adjusted to control the system for an output of heat enough in excess of actual requirements to take care of the variable factors of wind, heat from the sun, etc.

place.-

Because of this mode of operation, there is a close correspondence between the temperature of the heating medium and the requirement for heat of the space to be heated, and this regardless of changes of outside temperature. The fluctuations in room temperature incident to the intermittent accelera tion and retardation of the fire and resulting from the delay in the response of the system to temperature changes in the space heated,

are reduced to a minimum. The temperature curve of the heating medium, instead of periodically rising considerably above and then falling considerably below the straight line representing the required temperature level, closely approximates such line.

It may be stated that contact 18 of the room thermostat 16 could be eliminated. It has no function so far as the method of control is concerned.= In practice the thermostat has this upper contact as a measureof safety in case the compound thermostat should fail to function.

In Fig. 2 a similar method but with some -modification is applied again to a hot water heating system. The furnace 35 in this form of the invention isindicated as an oil-burning furnace. actuates a control device 36 for controlling the supply of fuel to the furnace. In this arrangement the bulb 37 of the compound thermostat 20, which is to. be subjected to fluctuations in the temperature of the heating medium, is clamped to the return pipe 38 from the radiating system, represented by radiator 39, to the boiler of the steam generator. The wiring arrangements are the same The thermostatic mechanism as in Fig. 1. By associating the bulb. 37 with the return pipe, the water throughout the circulating system will have to be raised'to a lows: 'wire 40, high temperature contact 18 certain point before thermostat will function to retard the fire.

' In Fig. 3 the methodutilizes the control correlation (2) mentioned above. In this embodiment. of the invention either the room thermostat 16 or the compound thermostat 20 will function to accelerate the fire, whichever thermostat closes its circuit first; but

- both must close their circuits in order that the fire be retarded. The system insures a quick heating up of the room when the system isfirst started up, for example. Italso positively eliminates cold 70. vThe radiator a separate safety temperaturelonce the system is balanced)- and the low temperature point 68.- The compound: thermostat '20 may be set for low temperature actuation at 170.

temperature actuation at 150 F. and high These temeratures are of course merely illustrative.

en the system is started up in the morning the movable contact members 19 and 23 will'be against their respective low temperature contacts. Ordinarily the heating medium will heat up to the high-temperature point of thermostat 20 before the room.tem-

perature has brought the movable contact member 19 against the hi 'h temperature contact 18. However the fire will not be retarded until both movable contact members are against their respective high temperature contacts. When this occurs the firewill be retarded by. the closing of a, circuit as folof the room thermostat 16, movable contact member 19, wire 41, high temperature contact 22 of compound thermostat 20, .movable 'contact'member 23 and wire42.' The fire will again be accelerated as soon as the heatt ing medium cools to 150 'F. or if before that time the room temperature should fall to68' F. The circuit throughthe low tem perature contact of the compound thermostat is as follows: wire 43, low temperature contact 21, movablecontact member 23 and wire 42. The circuit through the 'low temperature contact of the room thermostat 16 is as follows: wire 43, wire 44; low temperature contact 17 of thermostat 16,- movable contact member 19, wire 41, high temperature contact 22 of "thermostat 20, movable contact member 23, and wire 42. Thus the room thermos'tat may bring about an acceleration of the fire even if the temperature of the medium has been previously raised to such a point as to cause thermostat 20 to bring about a retardation of the fire; that is, if the temperature of the medium in rising has reached-170 "However, this situation will not ordinarily be presented. Once the heating system isin operation movable contact member 19 will oscillatein proximity to the high temperature contact 18,'bringing about a retardation of the fire when the circuit isbroken at this point and an acceleration of the fire, through operation of the compound thermostat, when the circuit is closed. In short, there will be point control but as between movable contact member 19 and the high temperature contact I The system shown in Fig. 4' combines the control methods of the systems shown in Fig.

tact 21 and high temperature contact 22, a

contact plate 45', with'which the movable contact member 23 is in contact except just before it is moved against contacts 21 or 22.

To illustrate a particular case, assume that the room thermostat 16 is set fora high'temperature of 70 and a low temperature of 68 and the compound thermostat (in the case of a hot water system) for a high tem perature of 170 and a low-temperature of 150. The drawinglillustrates the positions of the movable contact members when the fire is first started up. Ordinarily the heating medium will heat to 17 0 before the room temperature reaches 70. In that case the fire will be retarded by the closing of a circuit as follows: wire 46, movable contact member 23 and thermostat 20, high temperature contact 22, and wire 47.

However, if the room temperature reaches 70 before the heating medium is elevated to 17 0 the fire will be retarded by closing of a circuit as follows: wire 47, Wire 48, high temperature contact 18 of the room thermostat 16, movable contact member 19, wire 49,

contactplate 45, movable contact member 23 (which, except for extreme positions, will be on contact plate 45) and wire 46.

As soonas the water falls to 150 a circuit is closed, bringing about an acceleration of the fire, this circuit bein as follows: wire 46, movable contact member 23 of thermostat 20, low temperature contact 21, and wire,

50. Ordinarily the fluctuations of temperature between the limits for which the thermostats are set will be more rapid in the heating medium than in the space heated, so that-the compound thermostat will control the system subject to the making and breaking at 191 8 of the circuit through the room lull thermostat. H0wever,'if on falling temperatures the room thermostat acts first it will accelerate the fire by the closing of a circuit as follows: wire 50, wire 51, low temperature contact 17 of thermostat contact member 19, wire 49, contact plate 45, movable contact member 23 of thermostat 20 and wire 46. The gaps between the contact plate and contacts 21 and 22 of thermostat 20 provide appreciable intervals of time between the actuations in opposite senses of the control apparatus by the two thermostats. This correlation of the controls insures maintenance of room temperature at a fixed point, eliminating any possibility of cold 70, besides insuring a quick heating up of the room when the system is started up and also puts an upper limit on the water temperature so that an additional safety device on the boiler is not required.

Fig. 5 illustrates the application of the method to control of a vacuum or vapor steam system. The thermostats and their wiring are the same as shown. in Figs. 1 and 2 (although the systems of Figs. 3 or 4 might be used). The furnace is indicated as an oil burning furnace. The bulb 52 of thermostat 20, which is responsive to temperature fluctuations of the heating medium, is associated with the radiator 53,. which is the most remote from boiler 35. The bulb is shown as clamped to the inlet pipe 54 to radiator 53. It might be otherwise-placed so as to respond to the temperature fluctuations of the medium at approximately this place in the radiating system. The purpose is to insure the complete filling of the radiating system with steam before the compound thermostat is actuated to retard the fire and the continuous operation of the system at outside temperatures above the temperature at which the'operation of the ordinary vacuum system, for example, ceases to be continuous.

The bulb 52 is preferably half the size of the outdoors bulb 28. This provides for a reduction in radiator temperature of 2 for every one degree increase in outdoors temperature. This is a customary gradient used in vacuum systems.

The system will permit the fire to operate in the morning until the room thermostat has functioned to retard the-fire, or until the systemis freed of air and the medium in the last radiator, the one most remote from the boiler, has reached a point at which the compound thermostat 20 will retard the fire.

Fig. 6 illustrates the application of the --method to a hot air heating system. The 1 th th t t i th th room,

thermostats and their wiring are the same as in Figs. 1 and 2 (although the arrangements of Figs. 3 or 4 might be substituted) but the bulb 55 of the thermostat 20 is arranged in'th'e hot air flue of the'furnaee' 56,

57 designating one of the hot air pipes 57 of the-furnace leading to the u ual register 58. Fig. 7 illustrates the app cation of the method to the control of anindirect heating s Y 16, movablein which the heating medium,

the water temperature reaches 120.

room thermostats 66, 67 are located in difi'ersystem. The thermostats and their wiring are shown the same as in Fig. 1. The bulb 59 of the compound thermostat 20 is arranged in the hot air duct 60 leading to the space 61 to be heated. 62 designates a steam or hot water radiator arranged to heat the air passing'through duct 60.

Fig. 8 illustrates the application of the method as applied to the control of a system hot water, for example, is heated by a plurality of fluid fuel, for'example, oil burners, two of such burners being shown. Each burner is controlled by the combined action of a room thermostat and a compound thermostat, the latter being set so that they function at different water temperatures. The room thermostats function preferably at the same high and low points, for example 72 and 70. The wiring of the control apparatus for each burner may be the same as shown. in Fig. 1. The furnace is designated 63 and has two burners, which, with their fuel controlling devices, are designated 64, 65. The room thermostats 66, 67 are preferably located in different rooms 68, 69. The compound thermostat 70 may be set to function at 158 F. and 168 F., for example, with an outside temperature of 0 F. The compound thermostat 71 may be set to function at 160 and 170 F. Each thermostat has an outdoors bulb 72 and a bulb 73 in the water space of the boiler 63 or elsewhere in the water system as may be desired. Under'these conditions, (assuming the system as being started up) and assuming, say, an outside temperature of 50 F., thermostat 70 will retard the fire by shutting off burner 64 when the water temperature reaches 118.

The other burner continues to operate. This burner is shut 03, however, as soon as The out parts of the house. If the temperature in either of these rooms reaches the upper critical temperature for which the room thermostat is set, the thermostat will operate to shut off the burner which it controls. In this system the acceleration and retardationof the fire is by increments and decrements,

roportioned to the maximum intensity of the fire, depending upon the number of burners individually controlled. One' advantage is that if a window is opened in one of the rooms 68, 69, artificially stimulating the fire, the effect will be counteracted by action of same as in Fig. 1. The bulb of thermostat 20,

responsive to temperature fluctuations in .the heating medium, is arranged to extend longitudinally through one of the radiators designated -74, as indicated at Thermo- In this arrangement, therefore, the amount ofradiating surface under steam depends upon theoutside temperature as affecting bulb28. v A a It will be obvious from the above specific. embodiment-s ofthe' invention that it is capable of application to practice in many di f-' ferent ways. The invention, therefore, is not to be considered as limited to any particularform of apparatusdput resides in the method .of control common to. all' of theftypical installations; chosen for illustration. The terms acceleration and retardation as applied to the fire are intended to include the turnin on of agas or oil flame and the shut; ting 0 of the same, in the case of furnaces of this .type.,'as' well as the increase or diminution of the flame as in Fig. 8..

of my copending application," Serial No. 244,225, filed January 3, 1928. t

I claim:

1. Method-of heating which-comprises controlling the introduction of heat to the space heated In accordance with temperature fluctu-- heated in accordance with temperature flucwhich the heating medium 'efiects its control in accordance with temperature changes of the outside atmosphere.

2. Methodof heating which comprises controlling the i'ntroduction of heat to the space 'ations of said space-and also of the heating -medium, and'ivar'ying the temperatures'at which the heating medium eifects itscontrol I inversely with respect to the rise and tall of outside temperature. I

3. Method ofheating which comprises controlling the introduction of heat to the space heated in response to temperature fluc'tuations of said space and also 'in response to fluctuations in the average of the temperatures of the heating medium and of the out-- side atmosphere,

4. Method of. heating which comprises" maintaining theheating medium at a temperature,"by. acceleration and retardation of the fire, between hi hand low critical temper- V atures whenever t e space heated-is below side temperatures.-

tuations of said space and also of the heating medium, and varying the temperatures at' the desired temperature, which'said critical perature, and decreasing the generation of heat whenever the temperature ofsaid space reaches a determinable maximum.

' 5. Method of heating which comprises controlling the acceleration and retardation of the fire at critical low and high temperatures of the medium variedinversely with respect to changes in outside'tem erature, and making the control brought a out at'one of-said .critical temperatures dependent upon a determinate temperature condition in the space heated.

6. Method of heating which, comprises inv creasing the introduction of heat tothe space heated whenever the temperatures both of said space .and ofthe heating medium,

in rising, reachesa critical high temperature, and varying v the critical temperatures at whichthe heating mediumefi'ects its control falling, reach critical low temperatures, de- 'i creasing the application of heat to said space when the temperature of the heating medium,

inversely with respect to rise andfall of outv I 7. Method of heating which comprises in creasing the introduction of heat to the space, I

heated whenever the temperatures both of the This apphcation is a continuation in part creasing the introduction of heat to the space.

heatedwhen the temperatureof the heating medium, in falling, reaches a critical low temperature and decreasing the introduction of heat when the temperatures. both of the heating medium and of the space heated, in rising, reach critical high temperatures and vary ng the temperatures at which the heatingmedium efiects its control in accordance with temperature changes of the outside atmosphere.

9. Method creasing the introduction of heat to the space of heating which-comprises inr 1 2o -heated when the temperature either of the heating medium or. of the space heated, in falling, reaches a critical low temperature,'

. anddecreasing the introduction of heat when the temperatures, both of the heating medium and of the space heated, i 1i rising,* reach critical hightemperatures, and varying the tem-- .peratures at which the' heating medium effects its control in accordance with temperature changes of the outside atmosphere.

which the movable contact member moves but so as to be free therefrom whenagainst the high and low temperature-contacts; said high and low temperature contacts of the compound -thermostat being I in circuits, closed by the movable jcontact member of said thermostat which are independent of the room thermostat and the high and low 15. Method of heating which comprises applying heat to the space heated, whenever the temperature in said space is below'that desired, at a rate slightly higher than the normal rate required to keep the space heated at the desired temperature, reducing said rate of heat applicatiom'whenever the temperature in said space is above that desired, to a rate slightly lower than the normal rate required to keep the space heated at the de-' sired temperature, and determining said rates of heat application by, and in accordance with, the outdoor temperature and the temperature of the heating medium.

IFRED I. RAYMOND.

temperature contacts of the room thermostat being in circuits, tact members, of said thermostats which include the intermediate'contact of the compound thermostat.

11. Method of heating which comprises controlling the introduction'of' heat to the iipace heated in accordance with temperature uctuations of said space and also of the v heating medium, and varyin the-temperatake place in outside atmos perature in sai applying heat to'the normal rate required to keep t ed at the desired temperature, reducing sald' tures at which the heating me control whenever any substantial changes here temperatures and in accordance wit such-chan es.

12.- Method of heating-which comprises controlling the introduction of heat to the space'heated .in accordance with temperature fluctuations of said space and also of the heating medium, and automatically varymg the temperatures at which the heating,

' control in accordance medium effects its with fluctuations in outside temperature.

13. Method of heatingvwhich comprises e temperature in said space is belowthat desired, at a rate slightly hi her than the e space heatum effects its space heated, whenever closed by the movable conrate of heat apiplication whenever the tem- 7 space is above that'desired and determining said first named rate oi heat ap lication by, and in accordance with, the outgoor temperature and the tempera-- ture' of the heatin medium.

14. Method of eating which comprises applying heat to the space heated, whenever the temperature in said space is above that desired,'at a rate slightly lower than the normal rate required to keep the space heated at the desired temperature, increasing said rate of heat application whenever the temperature in said space is below that desired, and determining said first named rate of heat application by, and in accordance with, the outdoor temperature and the temperature of the heating medium. 

